U.S. patent number 4,437,938 [Application Number 06/284,153] was granted by the patent office on 1984-03-20 for process for recovering ethylene oxide from aqueous solutions.
This patent grant is currently assigned to The Halcon SD Group, Inc.. Invention is credited to Vijay S. Bhise, Robert Hoch.
United States Patent |
4,437,938 |
Bhise , et al. |
March 20, 1984 |
Process for recovering ethylene oxide from aqueous solutions
Abstract
Ethylene oxide is recovered from aqueous solutions by extracting
with carbon dioxide in the near-critical or super-critical state,
thereby selectively removing the ethylene oxide from water, and
thereafter recovering ethylene oxide from the carbon dioxide by
distillation or other suitable means.
Inventors: |
Bhise; Vijay S. (Bloomfield,
NJ), Hoch; Robert (Ridgewood, NY) |
Assignee: |
The Halcon SD Group, Inc. (New
York, NY)
|
Family
ID: |
23089063 |
Appl.
No.: |
06/284,153 |
Filed: |
July 17, 1981 |
Current U.S.
Class: |
203/14; 203/42;
203/43; 203/49; 203/70; 549/541 |
Current CPC
Class: |
B01D
11/0407 (20130101); C07D 301/32 (20130101) |
Current International
Class: |
B01D
11/04 (20060101); C07D 301/00 (20060101); C07D
301/32 (20060101); B01D 003/34 (); C07D
301/32 () |
Field of
Search: |
;260/348.37
;203/43,68,70,67,14,49,42,91 ;422/256-260 ;196/14.52 ;210/634,511
;202/169 ;549/541 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
1290117 |
|
Sep 1972 |
|
GB |
|
1388581 |
|
Mar 1975 |
|
GB |
|
2032789 |
|
May 1980 |
|
GB |
|
2059787 |
|
Apr 1981 |
|
GB |
|
Other References
Stahl et al., Angew. Chem. Int. Ed. Engl. 17, pp. 731-738, (1978).
.
J. Am. Chem. Soc., 58, 1099, (1954), Francis, A. W..
|
Primary Examiner: Bascomb, Jr.; Wilbur L.
Attorney, Agent or Firm: Long; William C. Stewart; Riggs T.
Wells; Harold N.
Claims
What is claimed is:
1. A process for recovering ethylene oxide from aqueous solutions
comprising:
(a) contacting said aqueous solution of ethylene oxide with a
solvent comprising carbon dioxide in the near-critical or
super-critical state to selectively absorb ethylene oxide relative
to water and;
(b) separating the ethylene oxide-containing carbon dioxide of (a)
from the ethylene oxide-depleted aqueous solution and
thereafter;
(c) recovering the ethylene oxide from the separated ethylene
oxide-containing carbon dioxide of (b).
2. A process of claim 1 wherein said recovery process of (c)
comprises reducing the pressure of step (b) and distilling the
carbon dioxide from the ethylene oxide.
3. A process of claim 2 wherein the pressure of steps (a) and (b)
is about 35-300 kg/cm.sup.2 gauge and the pressure of step (c) is
about 30-75 kg/cm.sup.2 gauge.
4. A process of claim 1 wherein an adulterant gas is included
during recovery step (c) to increase the critical temperature of
the mixture.
5. In the process for recovering ethylene oxide from the gaseous
effluent of the vapor-phase catalyzed oxidation of ethylene where
said ethylene oxide is absorbed from said gaseous effluent into an
aqueous recirculating stream and thereafter recovered from the
ethylene oxide-rich aqueous stream, the improvement which comprises
contacting said ethylene oxide-rich aqueous steam with carbon
dioxide in the near-critical or super critical state to selectively
absorb the ethylene oxide.
6. A process of claim 5 wherein the pressure of said carbon dioxide
contacting is about 35-300 kg/cm.sup.2 and the temperature is about
0.degree.-100.degree. C.
Description
PRIOR ART
The invention relates to the recovery of ethylene oxide from
aqueous solutions. In particularly useful aspect, the invention
relates to the separation of ethylene oxide from aqueous solutions
formed when the gaseous effluent from the vapor-phase catalyzed
oxidation of ethylene is contacted with a recirculating aqueous
solution. Typically, these solutions are separated by distillation,
at a substantial cost for the energy required.
The effluent from the oxidation of ethylene, which is typically
carried out at 10-40 kg/cm.sup.2 gauge and 200.degree.-400.degree.
C. is contacted with water to absorb the ethylene oxide from the
gases, which can then be recycled to the oxidation reactor. This
absorption in water is typically carried out at a pressure near
that of the reaction and the ethylene oxide-rich aqueous stream
which results is at a fairly low temperature, about
30.degree.-100.degree. C., and is quite dilute in ethylene oxide,
typically about 0.5-5%. Recovery of pure ethylene oxide from water
is an energy-intensive process if done by conventional distillation
or the combination of distillation and water reabsorption as taught
for example in U.S. Pat. Nos. 3,418,338, 3,964,980, and 4,134,797.
A substantial reduction of the energy required can be achieved by
the extraction process of our invention.
The use of normally gaseous materials in their near-critical or
super-critical states as solvents has been known, especially in
connection with the separation of hydrocarbon mixtures, such as is
disclosed in U.S. Pat. No. 1,805,751. Interest in such separations
has revived recently since extractions with near or super-critical
fluids may take place at relatively low temperatures and with the
expenditure of less energy than is used by more conventional
methods of separation. The terms "near-critical" and
"super-critical" are well known to those skilled in the art. For
purposes of the present invention, these may include reduced
temperatures in the range of about 0.6-1 (i.e. near-critical) and
about 1-3 (i.e. super-critical).
A general discussion in Angew. Chem. Int. Ed. Engl. 17, p. 731-738
(1978) of the possibility of recovering various organic compounds
by super-critical gases mentions the pyrones, which are high
molecular weight epoxides, but are not oxirane compounds. Oxirane
compounds, such as ethylene oxide, are not mentioned.
The use of (near) super-critical fluids for separating compounds
from aqueous solutions has been less commonly discussed. For
example, in U.S. Pat. No. 3,969,196 it is shown that ethylene is
not capable of absorbing ethylene glycol and ethyl alcohols from
their aqueous solutions while higher alcohols can be recovered.
Francis, in J. Am. Chem. Soc., 58, p. 1099 (1954) disclosed that
carbon dioxide near its critical point has only slight ability to
absorb ethylene glycol and water but is completely miscible with
ethyl alcohol. No mention of ethylene oxide was made.
In British Pat. No. 1,290,117 the use of carbon dioxide to
extractcaffeine from aqueous solutions suggests that moist carbon
dioxide in the super-critical state has the properties of a polar
fluid and is able to take up polar compounds, such as caffeine.
Recovery of acrylic acid from aqueous solutions with carbon dioxide
is disclosed in U.S. Pat. No. 4,253,948, which features the
rejection of water taken up in the carbon dioxide by the formation
of hydrates.
Various agricultural products have been treated with super-critical
carbon dioxide, as for example in U.S. Pat. Nos. 3,806,619,
3,843,824, 3,939,281, and 3,923,847 and British Pat. No.
1,388,581.
The recovery of carboxylic acids from dilute aqueous solutions of
their alkali metal salts with super-critical carbon dioxide is
disclosed in U.S. Pat. No. 4,250,331. The carbon dioxide reacts
with the salt to form the acid, which is extracted by carbon
dioxide. It is suggested that other, more polar, super-critical
fluids may be added as needed to improve the solubility of certain
acids in carbon dioxide.
Published British application GB No. 2,059,787A discloses a process
for separating organic compounds, particularly water-miscible
oxygenated hydrocarbons, from aqueous solutions with super-critical
carbon dioxide and subsequent fractionation featuring the use of
vapor recompression to minimize the energy requirements for the
separation of the organic compounds from carbon dioxide. Although
alcohols, acids, aldehydes, esters, and ketones are mentioned
generally, the application of such a process to ethylene oxide is
not suggested.
Large amounts of water are required to absorb ethylene oxide, which
has a large activity coefficient in an ethylene oxide-water
mixture. Improved processes for recovering ethylene oxide have been
sought, particularly since the distillation of dilute aqueous
solutions has become more costly. It has now been found that the
extraction of ethylene oxide by (near) super-critical fluids,
specifically carbon dioxide, is feasible and provides advantages
over prior art recovery methods.
SUMMARY OF THE INVENTION
Ethylene oxide is recovered from aqueous solutions, especially
those formed by the contacting of the gaseous effluent of the
vapor-phase catalyzed oxidation of ethylene with recirculating
aqueous streams, by contacting such aqueous solutions with solvent
in the super-critical or near critical state, specifically carbon
dioxide. The conditions of the contacting are chosen to selectively
extract ethylene oxide from water into the solvent. Thereafter, the
ethylene oxide-rich solvent is separated from the ethylene
oxide-lean aqueous solution and the ethylene oxide recovered from
the solvent by distillation or other suitable means.
In a preferred embodiment, carbon dioxide at a temperature in the
range of about 0.degree.-100.degree. C. and a pressure in the range
of about 35-300 kg/cm.sup.2 gauge is brought into contact with an
aqueous ethylene oxide solution containing about 0.1-10 mol %
ethylene oxide. The carbon dioxide selectively extracts ethylene
oxide to an extent determined by the operating conditions,
typically above 90% is removed from the aqueous solution. The
ethylene oxide-rich carbon dioxide is physically separated from the
depleted aqueous solution, which remains a distinct liquid phase
and thereafter the ethylene oxide-rich solvent is subjected to
changes in temperature and/or pressure such that ethylene oxide may
be recovered. In one embodiment, the pressure of the ethylene
oxide-rich carbon dioxide will be reduced to about 30-75
kg/cm.sup.2 gauge and the carbon dioxide distilled off and recycled
to recover additional ethylene oxide.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram illustrating the process for catalytic
oxidation of ethylene to ethylene oxide and its recovery.
FIG. 2 shows an application of the process of the invention to the
recovery of ethylene oxide from high pressure aqueous
solutions.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The use of (near) super-critical fluids such as carbon dioxide is
especially useful in the recovery of ethylene oxide from the
aqueous solutions which commercial ethylene oxide plants usually
produce. Ethylene is oxidized in the vapor-phase by passing it
along with molecular oxygen and diluents, such as nitrogen or
methane, over a supported silver catalyst. The ethylene oxide
typically is recovered by absorbing it in water.
The conventional ethylene oxide process is illustrated
schematically in FIG. 1. Ethylene (10) and oxygen (12) are fed to a
catalytic oxidation reactor(14) employing a supported silver
catalyst, which is disposed inside tubes surrounded by a heat
transfer fluid used to remove the heat of reaction. Only a fraction
of the ethylene is converted to ethylene oxide in each pass through
the reactor and consequently a significant amount of ethylene is
usually recycled, along with diluent gases, such as nitrogen or
methane, to the reactor. Gases leaving the reactor via line 16 at
about 10-40 kg/cm.sup.2 gauge and 200.degree.-400.degree. C. are
passed to a high pressure absorber (18) where they meet a recycling
water stream (20) and are quenched and the ethylene oxide is
absorbed, along with carbon dioxide and various impurities produced
in the oxidation reactor. The gases which are not absorbed are
separated from the aqueous ethylene oxide solution and recycled via
line 22 to the reactor (14). The ethylene oxide-rich solution is
sent via line 34 to a stripper (26) where ethylene oxide is
separated and the lean water recycled via line 20 to the high
pressure absorber (18). After this, the gaseous ethylene oxide may
be absorbed again in a suitable solvent such as water or ethylene
carbonate and separated from various impurities, by methods which
are shown in this figure generally as purification (28), but which
may include those in the U.S. patents previously mentioned. The
final product may be substantially pure ethylene oxide as
indicated, or alternatively, a mixture of ethylene oxide and carbon
dioxide could be produced suitable for preparation of ethylene
carbonate.
FIG. 2 illustrates one embodiment of the invention. An aqueous
solution containing about 0.1 mol % (max. about 10 mol %) ethylene
oxide is available from the high pressure absorber (18) of FIG. 1
at about 10-40 kg/cm.sup.2 gauge and 50.degree.-100.degree. C. For
purposes of this example, the pressure is about 20 kg/cm.sup.2
gauge and the temperature 60.degree. C. Rather than stripping the
ethylene oxide as shown in the conventional process of FIG. 1, the
aqueous solution is supplied via line 30 to a mixing column 32
where it passes in countercurrent manner against a stream (34) of
carbon dioxide at near critical or super-critical condition,
selected so as to selectively extract above 90% of the ethylene
oxide. Smaller fractions could be extracted, but less complete
removal of ethylene oxide may not be economically advantageous. The
critical conditions for carbon dioxide are 31.degree. C. and 75.1
kg/cm.sup.2 gauge so that the extraction will be carried out at
temperatures in the range of about 0.degree.-100.degree. C. and
35.degree.-300 kg/cm.sup.2 gauge. In this example, the pressure is
about 88 kg/cm.sup.2 gauge and the temperature about 32.degree. C.
By proper selection of the amount of carbon dioxide and the
operating pressure and temperature, substantially all of the
ethylene oxide can be extracted while the bulk of the water is
rejected. In this example, about 35 mols of carbon dioxide per mol
of ethylene oxide is used and substantially all of the ethylene
oxide is absorbed. Despite the relatively large amount of water,
less than about 1% will be picked up by the carbon dioxide by
absorption, entrainment and the like under the optimum conditions
for extraction of ethylene oxide. The presence of this water is
neglected for purposes of the present example. Thus, a
substantially complete separation is made. The equipment employed
for this contacting will be familiar to those skilled in the art
and may include staged mixing in a sequence of vessels, but
typically a stirred mixing column (as shown) or a tower equipped
with trays or packing would be used.
The lean aqueous solution is returned to the absorber via line 36
after the net production of ethylene oxide has been removed. The
carbon dioxide rich in ethylene oxide (about 2.9 mol %) is sent via
line 38 from the contacting stage (32) to a separation stage (40)
for removal of the ethylene oxide. The separation may be carried
out by various procedures, depending particularly upon the
operating conditions. The figure illustrates one suitable method
for making the separation. The ethylene oxide-carbon dioxide
mixture is passed to a distillation column (40) where the two
constituents are separated, with the carbon dioxide being condensed
in exchanger 42 and returned as reflux via line 44 and sent via
line 34 and compressor 46 to the extraction column 32 and ethylene
oxide plus some carbon dioxide and impurities and by-products being
sent via line 48 to further purification steps. It is the intention
of the figures to illustrate the situation in which the operating
pressure is reduced across a valve 39 (although an expander could
be used to recover power) so that the absorption capacity of the
carbon dioxide is reduced and ethylene oxide can be separated. The
operating pressure for the distillation would be selected to remain
near the critical value to take advantage of the reduced latent
heat of vaporization, but could be in the range of 30-75
kg/cm.sup.2. For this example, the pressure is about 73 kg/cm.sup.2
gauge. The pressure may be about 70-75 kg/cm.sup.2 gauge if pure
carbon dioxide is used and the operating temperature at the bottom
of the column would be less than about 50.degree. C. (depending
upon pressure) and at the top 0.degree.-50.degree. C. For this
example, the bottom temperature is about 43.degree. C. and the top
temperature is about 30.degree. C.
Under the conditions described it may be difficult to economically
condense carbon dioxide without refrigeration and adulterant gases,
such as propane or butane, which have higher critical temperatures
than carbon dioxide, may be used to increase the critical
temperature and pressure of the vapor mixture at the top of the
column, thus making possible more economical condensation.
Other operating techniques are considered within the scope of the
invention, for instance the method disclosed in GB No. 2,059,787A
in connection with the separation of other compounds from carbon
dioxide. It is also possible to adjust the temperature of the
ethylene oxide-rich stream to reduce the ability of the carbon
dioxide to absorb the ethylene oxide and, thus, permitting the
separation to be made. Broadly, speaking, the selection of the
method employed will be made based on the costs of each method as
affected by the physical properties which are associated with the
ethylene oxide-(near) super-critical fluid system being
considered.
The application of the invention need not be not confined to the
high pressure solution formed from the oxidation reactor effluent
as shown in FIG. 2 and discussed above. Other aqueous solutions of
ethylene oxide may be treated in the same manner, as for example
the solution produced when the high pressure solution is stripped
of ethylene oxide, which is then reabsorbed in water in
conventional ethylene oxide recovery. Those skilled in the art will
recognize there are various aqueous solutions to which the
extraction of ethylene oxide by (near) super-critical carbon
dioxide may be applied.
* * * * *